Digital Mobile Radio (DMR) standard is an European private network communication standard recently issued by European Telecommunications Standards Institute (ETSI) for taking place of the analog Private Mobile Radio (PMR) standard, which is advantageous in large coverage area, high transmission rate, high frequency spectrum efficiency, and good power saving effect. Therefore, mobile communication products based on DMR standard are highly favored in the market.
The DMR standard employs Time Division Multiple Access (TDMA) frame structure with double time slot. FIG. 1 is a schematic structural diagram of DMR TDMA frame in direct mode. The direct mode means that communication terminals communicate with each other directly without via a relay station therebetween. As shown in FIG. 1, a DMR TDMA frame includes two completely identical time slots, each of the time slots is 30 ms in length and is further divided by a middle synchronization pattern field in a length of 5 ms into two loads with the same length (11.25 ms bits). Each of the time slots is provided with a protective interval in a length of 1.25 ms at two ends thereof respectively. Therefore, the protective interval between the two time slots is 2.5 ms.
However, the DMR standard does not further define how to use two time slots in the frames to support two independent channels of private network communication in direct mode; therefore, the existing private network communication terminals based on the DMR standard still use one time slot in the frames for private network communication. FIG. 2 is a schematic diagram of an application environment 200 for existing private network communication terminals based on the DMR standard. As shown in FIG. 2, there are a plurality of private network communication terminals 202˜208 in the application environment 200. Wherein, the private network communication terminal 202 is communicating with the private network communication terminal 204. Though the private network communication between the private network communication terminal 202 and the private network communication terminal 204 only occupies one time slot in a DMR TDMA frame, the private network communication terminal 206 and the private network communication terminal 208 in the same geographic region still cannot use the other time slot to perform private network communication.
The cause for the above problem lies in: though the private network communication between the private network communication terminal 202 and the private network communication terminal 204 only occupies one time slot, the position of the occupied time slot is not fixed (i.e., the time slot occupied by the same channel of private network communication may vary at different times; for example, time slot 1 is used to initiate the private network communication, time slot 2 or time slot 1 may be used for a response in different response stages); therefore, other private network communication terminals in the same geographic region can not determine in advance which time slot is not occupied, and consequently can not initiate a new private network communication.
Hence, a technical solution is required to overcome the drawback existing in the prior art.